add public_on attribute to tests

Author: gr8bit

spec/serializers/alchemy/json_api/page_serializer_spec.rb

@@ -32,6 +32,7 @@
       expect(attributes[:language_code]).to eq("en")
       expect(attributes[:meta_keywords]).to eq("Meta Keywords")
       expect(attributes[:meta_description]).to eq("Meta Description")
+      expect(attributes[:public_on]).to eq(page.public_on)
       expect(attributes[:created_at]).to eq(page.created_at)
       expect(attributes[:updated_at]).to eq(page.updated_at)
       expect(attributes[:legacy_urls]).to eq(["/other"])